Historically, extraction and concentration of substances from test samples, such as leachates or environmental pollutants in water, soils for organic analysis, oil-soluble vitamins in grains, plasticizers in polymers, and drug related substances in blood serum, were carried out in separate extraction and concentration apparatus. Recently, it has become more common within the art to use combined extraction/concentration apparatus to reduce processing time, and to reduce the amount of solvent vapor released into the atmosphere when transferring the extractant from the extractor apparatus to the concentrator apparatus.
Extraction and concentration of a sample in a typical combination extractor/concentrator is conducted by passing a suitable solvent through a test sample repeatedly in order for the solvent to combine with any substance that may be present within the sample. After the sample has been adequately exposed to the solvent, a valve usually located along a tube connecting a sample containing body and a concentrator apparatus, is closed and the extract is concentrated by distilling away the solvent to render a concentrate of the substance contained in the solvent. The concentrate is then available for analysis.
When using solvent having a density lesser than the density of the sample in which it is being passed, a typical combination extractor/concentrator apparatus has an insert, or other means, within the sample containing body for introducing the solvent from below the sample in order for it to rise therethrough. Although such apparatuses are designed to accommodate the differing densities of the solvent and the sample, care must be taken to ensure that the proper levels of solvent and sample are maintained so the solvent and/or the sample does not back flow through the apparatus due to unequal head pressures.
Representative prior art combination extractor/concentrator apparatuses are shown in FIGS. 1 and 2. The apparatus shown in FIG. 1 is for use with solvent having a density greater than the density of the sample being processed. The apparatus shown in FIG. 2 is for use with solvent having a density lesser than the density of the sample being processed. The apparatus shown in FIG. 2 can be easily distinguished from the apparatus in FIG. 1 by the insert within the sample container body.
A shortcoming with prior art apparatuses includes the need for an elevated solvent connecting tube. An elevated connecting tube is required to balance the equation pertaining to hydraulic head pressures within the apparatus: sample height.times.sample density=solvent height=solvent density. Notwithstanding that an apparatus has been designed to achieve a balance within the above equation, the technician operating the apparatus is not relieved of the burden of ensuring that the respective amounts of solvent and sample present within the apparatus are within the design parameters of the apparatus.
A further shortcoming with prior art apparatuses is the need to have a relatively large pool of solvent underlying, or overlying, the sample liquid for achieving a hydraulic balance within the apparatus. In addition to the expense of obtaining large volumes of solvents, certain solvents may pose environmental threats if released to the atmosphere in large quantities.
There is also a long standing economic need within the art for the apparatus to perform extractions and concentrations within shorter time periods as compared with the time periods required with conventional, or more recently available combination extractor/concentrator apparatuses.
Therefore, there is a continuous need within the art, for extractor/concentrator apparatuses that operate efficiently and quickly with relatively small amounts of solvent.